A wide variety of coating compositions have been developed to protect metal surfaces from corrosion. Some of these coatings simply rely on the formation of an impenetrable barrier between the metal surface and the surrounding environment. Others include a corrosion-inhibiting filler or the like to prevent corrosion. For example, fillers such as zinc and lead have been used extensively in coating compositions to provide anodic protection against corrosion.
Such coatings require that the surface of the metal to be protected be scrupulously clean. Otherwise, the protection is lost either by loss of adhesion of the coating or by loss of contact between the corrosion-inhibiting filler and the metal. Thus, if the coating composition is to be applied to an already rusted surface, that surface must be first cleaned to remove virtually all of the rust. Typically, this is done by sand blasting or the like.
In many industrial situations, however, conditions such as cost, pollution, operation interruption, and the like do not permit extensive surface preparation. In such a situation, surface preparation may be limited to hand cleaning with, for example, a wire brush. This would remove large rust deposits but would not clean the surface sufficiently for the application of a conventional rust-inhibiting coating composition. In such a situation, the coating composition needs to dissolve rust in addition to inhibit rust formation.